Electronically switched dynamic brake for a dc motor

Claim 2

A dynamic braking circuit for automatically and substantially instantaneously initiating damping of the back e.m.f. of a DC motor driven in a first direction with a driving voltage of a first polarity from a DC source upon the driving voltage falling below the back e.m.f. of the motor, comprising: first means for conducting the driving voltage to the motor when the driving voltage is greater than the back e.m.f. Of the motor; damping means: second means operable in response to the driving voltage falling below the back e.m.f. of the motor for switching the back e.m.f. across said damping means; and means for reversing the driving voltage to be of a second polarity for driving the motor in a second direction, said second means being operable for conducting the second polarity driving voltage to the motor when the driving voltage is greater than the back e.m.f., said first means being operable in response to the second polarity driving voltage falling below the back e.m.f. of the motor for switching the back e.m.f. across the damping means, and said damping means including first and second damping devices, said first device being serially connected with said first means and said second device being serially connected with said second means.

Claim 3

The dynamic braking circuit of claim 1, wherein said first means is a diode serially connected with said motor for applying said first polarity voltage across said motor and for conducting driving current from said source to said motor, an wherein said second means includes an electronic switch having first, second and third electrodes, said first and second electrodes being current conducting electrodes connected in series with said damping means across said motor, said third electrode being a control electrode connected with said first electrode across said diode, and means for biasing said switch to a conduction state upon said driving voltage falling below the back e.m.f. of said motor.

Claim 4

The dynamic braking circuit of claim 1 wherein said first means comprises a first NPN transistor and a first PNP transistor having their base and emitter electrodes serially connected in a first direction with the motor across the source and further having their emitter and collector electrodes serially connected with said damping means across the motor, said second means comprises a second NPN transistor and a second PNP transistor having their base and emitter electrodes serially connected in a second direction with the motor across the source and their emitter and collector electrodes serially connected across the motor, wherein the bases of said first NPN transistor and said second PNP transistor are connected together to one terminal of said source, and the bases of said first PNP transistor and said second NPN transistor are connected together to the other terminal of said source.

Claim 5

The dynamic braking circuit of claim 1, wherein said damping means is a single device serially connected with said motor to provide equal dynamic braking rates for each direction of rotation of said motor.

Claim 6

The dynamic braking circuit of claim 1, wherein said first and second damping devices have different values to provide differential braking rates for each direction of rotation of said motor.

Claim 7

The dynamic braking circuit of claim 1 wherein said first means comprises a first diode and first electronic switch having first, second and third electrodes, said first diode and said first and third electrodes of said first switch being serially connected with said motor in a first direction, said second means comprises a second diode and second electronic switch having first, second and third electrodes, said first and third electrodes of said second switch and said second switch and said second diode being serially connected with said motor in a second direction, said first and third electrodes of said second switch being connected across said first diode, said first and third electrodes of said first switch being connected across said second diode, said first and second electrodes of said first switch being connected across said motor, said first and second electrodes of said second switch being connected across said motor, means for biasing said first switch to conduct damping current from said motor to said damping means upon said source voltAge falling below said back e.m.f. of said motor during rotation in the first direction, and means for biasing said second switch to conduct damping current to said damping means upon the source voltage falling below the back e.m.f. of the motor during rotation of said motor in the second direction.

Claim 8

The dynamic braking circuit of claim 6, wherein said first and second electronic switches are PNP transistors, and said first, second and third electrodes of each transistor is an emitter electrode, a collector electrode and a base electrode respectively.